The use of recycled fibers is becoming an important aspect of papermaking for economic and environmental considerations. The preliminary manufacturing steps in the use of recycled fibers for papermaking consists of repulping the paper sources, then removing the printing inks from the fibers. A typical deinking process utilizes a combination of chemical and mechanical techniques in several stages. Large amounts of water are used in the washing or flotation stages, wherein chemically treated ink particles and other contaminants are physically removed from the fibrous slurry. The wastewater, or effluent, from these stages is typically recycled back into the mill for reuse in the deinking process. As the recycled effluent contains dispersed inks, fiber fines and inorganic fillers, these contaminants must be removed to provide a clean water source for the deinking process and to prevent the dispersed inks from being reintroduced into the fibers. The effluent may also be discharged from the mill; thus, suspended solids must be removed from the wastewater to meet environmental regulations.
Clarification chemicals are typically utilized in conjunction with mechanical clarifiers for the removal of solids from the effluent. Clarification generally refers to the removal of nonsettleable material by coagulation, flocculation, and sedimentation. See the Betz Handbook of Industrial Water Conditioning 9th Edition, 1991, Betz Laboratories, Inc., Trevose, Pa., pages 23 through 30.
Coagulation is the process of destabilization by charge neutralization. Once neutralized, particles no longer repel each other and can be brought together. Coagulation is necessary for removal of colloidal sized suspended matter. Flocculation is the process of bringing together of the destabilized, "coagulated" particles to-form a larger agglomeration or floc. Sedimentation, or settling, refers to the physical removal of particles from suspension that occurs once the particles have been coagulated and flocculated. Sedimentation alone, without prior coagulation results in the removal of only relatively coarse suspended solids.
The clarification chemicals utilized in conjunction with mechanical clarifiers coagulate and/or flocculate the suspended solids into larger particles, which can then be removed from the effluent by gravitational settling or flotation. Depending upon the characteristics of the individual effluent, differing chemical types and programs may be utilized.
Clarification studies performed on newsprint deinking effluent indicates that these systems have a large anionic charge demand, requiring the use of a dual polymer system for effective clarification. A dual polymer system operates upon a Patch Model Method as described in Pulp and Paper, 3rd Edition, Volume 3, James P. Casey, at pages 1597 to 1599. The patch model system typically comprises a low molecular weight cationic coagulant in combination with a high molecular weight anionic flocculant.
The use of vinylamine copolymers for flocculation in water treatment is known. U.S. Pat. No. 4,217,214 discloses the use of high molecular weight polyvinylamine hydrochloride as a flocculating agent in treating water systems. Polyvinylamine hydrochloride is an ethenamine hydrochloride homopolymer, CAS Registry No. 29792-49-2.
U.S. Pat. No. 4,808,683 discloses the use of a mixture of a vinylamine copolymer of the formula disclosed therein as a flocculating agent, drainage aid, and paper strength increasing agent.
U.S. Pat. No. 4,957,977 discloses the use of a mixture of vinylamine copolymers of the formula disclosed therein as a flocculating agent and a paper strength increasing agent.